1. Field of the Invention
The present invention relates to a technique for filling liquid into bottles, cans or the like, particularly for use in a food filling machine, but also generally applicable for filling liquids other than foods, such as medical supplies, cleaning materials, oils, etc.
2. Description of the Prior Art
Known techniques for filling a predetermined amount of liquid food into a container such as a bottle, a can or the like include, (1) a piston type system for filling a predetermined volume, and (2) a system for filling a predetermined weight by measuring a gross weight including the weight of the container.
(1) The piston type fixed volume filling system of the prior art involves the following problems:
(a) Adjustment of the filled volume is achieved by adjusting a stroke of a piston, but the adjustable range is limited, and in the case of a multiple system it is necessary to finely adjust the individual piston strokes.
(b) In order to enhance the filling flow rate, it is necessary to speed up suction and ejection cycles, and thus filling precision is changed or degraded under the influence of material properties (density, viscosity, etc.) of the filled liquid. In addition, if the operation cycles are quickened more than a predetermined degree, then problems arise such that generation of cavitation upon suction and inertia of liquid flow become remarkable and cut-off of liquid is unstable. Thereby, it becomes impossible to fill a fixed volume.
(c) In the case where it is desired to fill a predetermined weight of liquid into a container such as a bottle, a can or the like, if the temperature of the liquid is varied, then the density of the liquid changes and hence the filled weight is varied.
(2) The system for filling a predetermined weight by measuring a gross weight including the weight of the container involves the following problems:
(d) In the case where it is desired to fill a relatively small weight into a bottle, a can or the like, since the liquid is weighed as a part of the gross weight including the weight of the container, precision of determining the net filled weight is degraded.
(e) In order to realize high efficiency (large capability) in metering and filling, after a container such as a bottle, a can or the like has been placed on a weighing section, stilling of the weighing section is necessary, and the time required for such stilling results in inefficient operation. Also it is necessary to pay attention so that any excessive weight or dynamic load will not be applied to the weighing section, and a handling mechanism which can achieve positioning of the bottle, a can or the like is necessary. To fulfil these requirements is especially difficult for a relatively small-sized container to be filled.